The following discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was published, known or part of the common general knowledge in any jurisdiction as at the priority date of the application.
There currently exist a number of devices for absorbing blast energy arising from high impact shock such as mine blasts. These devices are typically in the form of energy attenuation (EA) seats mounted within vehicles or hulls of armoured vehicles so that when a mine blast occurs, these EA seats serve to dissipate blast energy, minimizing injuries and preserving lives of personnel such as soldiers.
Existing EA seats typically comprise dampers such as mechanical springs mounted thereon to mitigate and dissipate blast energy experienced during a blast event. However, while possessing repeatability in terms of its damping properties, mechanical springs are not ideal for absorption of sudden blast energy due to their generation of rebound energy. Drop tests have revealed that, for a reasonably sized spring that does not bottom out on itself, the limits of mechanical spring based shocked attenuation has been attained even when the drop heights are relatively low, that is, the impact generated by the simulated drop height is much lesser that the impact and/or force generated during a mine blast.
An alternative to the use of mechanical spring is the use of deformable solids as energy dampers in EA seats. However, it is not easy to select an ideal deformable solid due to two competing objectives. On one hand, the deformable solid must be soft enough to attenuate shock, but on the other hand it must also be able be rigid enough to endure shock and vibration from daily handling from soldiers and operators such that its damping properties are not compromised as a result of daily operational usage or common usage pattern in military operations, where many a times personnel may jump on and off their EA seats, or when the vehicle carrying the EA seats goes over uneven terrain causing vibrational forces and shock to be transmitted to the EA seats, causing premature deformation of the deformable solids in the EA seats.
Besides blast energy absorption, another consideration in the design of EA seats is compactness and utilization of space that is crucial for an efficient and effective military. There exists in the current market supply foldable EA seats that are mounted either at the bottom of the vehicle hull or at the side. Such an arrangement allows the EA seat's backrest to be foldable, thus enabling users to quickly access and deploy the various payloads behind them once the backrest is folded towards the seat, as is common in military applications.
In comparison with bottom or side-mounted EA seats, blast mitigation is however better achieved when an EA seat is mounted to the ceiling of the vehicle. This is because during a mine blast, the ceiling of the vehicle typically experiences the least shock transmission compared to the rest of the hull and with much lesser local deformation. In this regard, local deformations are individual bumps on the vehicle hull that are caused by shock waves on localized regions. To date, however, no ceiling mounted EA seats could be folded down to permit access to payload behind seats. Existing design that allows the seat backrest to be folded down, such Armatec™ seats, still leaves behind a rigid and obstructing pillar that is bolted to the ceiling. This leads to configuration problems as it meant that payload distributed behind the troopers could not be easily accessed for rapid deployment crucial for military operations. This situation is further exacerbated if the payload items are bulky as in the case of rocket launchers and long-barrelled light arms.
Further, in order for an EA seat to be mounted to the bottom or sides of the vehicle hull, the mounting points might have to accommodate a high local deformation which often causes fasteners such as bolt heads to shear off as the hull bends away from the mounting surfaces. A seat mounted from the ceiling will only have to deal with the globalized acceleration caused by the vehicle being thrown upwards. Therefore, for proper shock attenuation, the EA seat should ideally be mounted on the ceiling.
In addition to the above, another issue with mounting the seat next to the sidewall of the vehicle is the relatively high amount of chordal vibration experienced by the crew. This is especially prevalent for tracked vehicle such as tanks, whereby rhythmic thumping of the tracks hitting the support rollers gets transmitted to the occupants.
Another consideration of an EA seat is weight. The general paradigm is that a true crushable rigid EA seat tends to be relatively heavier compared to a non-EA common/standard canvas seat due to the extensive use of metal frames as its structure. An average crush type EA seat hovers approximately 20 kilograms and upwards.
In view of the above-mentioned considerations and problems, there exists a need to improve existing EA seats to achieve an optimal combination of better EA properties, reduction in weight, and allowance of rapid access to payload at the same time.
The invention seeks to meet the needs at least in part.